Encyclopedia of

Heavy metal poisoning

Photo by: Eric Middelkoop

Definition

Heavy metal
poisoning
is the toxic accumulation of heavy metals in the soft tissues of the
body.

Description

Heavy metals are chemical elements that have a specific gravity (a measure
of density) at least five times that of water. The heavy metals most often
implicated in human poisoning are lead, mercury, arsenic, and cadmium.
Some heavy metals, such as zinc, copper, chromium, iron, and manganese,
are required by the body in small amounts, but these same elements can be
toxic in larger quantities.

Heavy metals may enter the body in food, water, or air, or by absorption
through the skin. Once in the body, they compete with and displace
essential
minerals
such as zinc, copper, magnesium, and calcium, and interfere with organ
system function. People may come in contact with heavy metals in
industrial work, pharmaceutical manufacturing, and agriculture. Children
may be poisoned as a result of playing in contaminated soil.

Demographics

Heavy metal poisoning is relatively uncommon. In children, lead ingestion
is the major culprit of heavy metal poisoning. In 2000, an estimated one
in 22 American children had high levels of lead in their blood. Children
in urban areas with old lead water pipes and lead-painted homes are
especially at risk. Mercury poisoning is possible from eating contaminated
fish.

Causes and symptoms

Symptoms will vary, depending on the nature and the quantity of the heavy
metal ingested. Affected people may complain of
nausea
,
vomiting
,
diarrhea
, stomach
pain
,
headache
, sweating, and a metallic taste in the mouth. Depending on the metal,
there may be blue-black lines in the gum tissues. In severe cases, people
exhibit obvious impairment of cognitive, motor, and language skills. The
expression "mad as a hatter" comes from the mercury
poisoning prevalent in seventeenth-century France among hat makers who
soaked animal hides in a solution of mercuric nitrate to soften the hair.

When to call the doctor

A healthcare professional should be contacted whenever exposure to any
heavy metal is suspected. The Centers for Disease Control and Prevention
(CDC) recommends testing all children for lead exposure at 12 months of
age and, if possible, again at 24 months. Testing should start at six
months for children at higher risk for
lead poisoning
.

Diagnosis

Heavy metal poisoning may be detected using blood and urine tests, hair
and tissue analysis, or x ray.

In childhood, blood lead levels above 80 mg/dL generally indicate lead
poisoning; however, significantly lower levels (>30 mg/dL) can
cause
mental retardation
and other cognitive and behavioral problems in affected children. The
Centers for Disease Control and Prevention considers a blood lead level of
10 mg/dL or higher in children a cause for concern. In adults, symptoms of
lead poisoning are usually seen when blood lead levels exceed 80 mg/dL for
a number of weeks.

Blood levels of mercury should not exceed 3.6 mg/dL, while urine levels
should not exceed 15 mg/dL. Symptoms of mercury poisoning may be seen when
mercury levels exceed 20 mg/dL in blood and 60 mg/dL in urine. Mercury
levels in hair may be used to gauge the severity of chronic mercury
exposure.

Since arsenic is rapidly cleared from the blood, blood arsenic levels may
not be very useful in diagnosis. Arsenic in the urine (measured in a
24-hour collection following 48 hours without eating seafood) may exceed
50 mg/dL in people with arsenic poisoning. If acute arsenic poisoning is
suspected, an x ray may reveal ingested arsenic in the abdomen (since
arsenic is opaque to
x rays
). Arsenic may also be detected in the hair and nails for months following
exposure.

Treatment

The treatment for most heavy metal poisoning is chelation therapy. A
chelating agent specific to the metal involved is given orally,
intramuscularly, or intravenously. The three most common chelating agents
are calcium disodium edetate, dimercaprol (BAL), and penicillamine. The
chelating agent encircles and binds to the metal in the body's
tissues, forming a complex; that complex is then released from the tissue
to travel in the bloodstream. The complex is filtered out of the blood by
the kidneys and excreted in the urine. This process may be lengthy and
painful and typically requires
hospitalization
. Chelation therapy is effective in treating lead, mercury, and arsenic
poisoning, but it is not useful in treating cadmium poisoning. As of 2004,
no treatment had been proven effective for cadmium poisoning.

In cases of acute mercury or arsenic ingestion, vomiting may be induced.
Washing out the stomach (gastric lavage) may also be useful. The affected
person may also require treatment such as intravenous fluids for
complications of poisoning such as shock, anemia, and kidney failure.

Prognosis

The chelation process can only halt further effects of the poisoning; it
cannot reverse neurological damage already sustained.

Prevention

Because exposure to heavy metals is often an occupational hazard,
protective clothing and respirators should be provided and worn on the
job. Protective clothing should then be left at the work site and not worn
home, where it could carry toxic dust to
family
members. Industries are urged to reduce or replace the heavy metals in
their processes wherever possible. For the sake of children's
health along with everyone else's, exposure to environmental
sources of lead, including lead-based paints, plumbing fixtures, vehicle
exhaust, and contaminated soil, should be reduced or eliminated.

Nutritional concerns

Parents should avoid preparing or serving food in containers that have
lead in their glazing.

Parental concerns

Parents living in homes built prior to 1978 should be vigilant in removing
flaking or peeling paint because it might contain lead. Simply repainting
such surfaces will not solve the problem. Parents must monitor the
environments in which their children
play
and the objects that go into their children's mouths. Cleanliness
is a must if old paint is in a child's environment. Removal
(stripping paint to bare metal or bare wood) of lead is the best way to
prevent lead exposure in children. Areas where removal is taking place
should be sealed off from the rest of the house. In addition, children
should be kept away from occupational sources of other heavy metals.
Parents
who are concerned about their child's exposure to lead should have
the child tested.

KEY TERMS

Chelation
—The process by which a molecule encircles and binds to a metal
and removes it from tissue.

Heavy metal
—One of 23 chemical elements that has a specific gravity (a
measure of density) at least five times that of water.